1. Technical Field of the Invention
The present invention relates to a sealing apparatus for a gas turbine and more particularly relates to a sealing apparatus for a gas turbine in which clearance variations in a sealing structure intervening between the inner shroud members of stationary blades and the platforms of moving blades are eliminated to improve sealing performance.
2. Description of the Related Art
FIG. 5 is a sectional view showing conventional sealing structure portions in a gas turbine. In the figure, reference numeral 21 denotes a moving blade, 22 denotes a platform thereof, 23 denotes a sealing plate, and numeral 24 denotes a blade root portion. A plurality of moving blades 21 are mounted radially around a rotor by way of the respective root portions 24. Reference numeral 31 denotes a stationary blade disposed adjacent to the moving blade 21, and numeral 32 denotes an inner shroud member of the stationary blade 31. Reference numeral 33 denotes a cavity defined inside of the inner shroud member, and numeral 34 denotes an annular shaped seal ring. Reference numeral 35 denotes an air hole provided in the seal ring 34 through which the cavity 33 and a space intervening between the stationary blade 31 and the blade root portion 24 of the adjacent moving blade 21 are communicated with each other. Reference numeral 36 denotes a sealing portion provided in the seal ring 34, wherein a labyrinth seal or the like is adopted to seal the rotatable root portion 24.
Reference numeral 37 denotes a honeycomb seal mounted on the inner shroud member at the upstream side thereof as viewed in the direction of the combustion gas flow, numeral 38 denotes a honeycomb seal also mounted on the inner shroud member 32 at the downstream side thereof. These honeycomb seals 37 and 38 are disposed in the vicinity of rotor arm portions 25a and 25b of the platforms 22 of the adjacent moving blades 21, respectively, and provide resistance to air leaks to thereby provide sealing.
This sealing structure will be described in more detail. FIG. 6 shows a portion D in FIG. 5 in detail. The honeycomb seal 38 having a large number of honeycomb cores is disposed at an end portion of the inner shroud member 32 in such a state that the open side of the honeycomb is positioned closely to a tip end portion of the rotor arm portion 25a of the platform 22. Moreover, a clearance t between the honeycomb seal 38 and the rotor arm portion 25a is substantially 1 mm.
In the above mentioned sealing structure, the air 40 leaking at a high pressure from the cavity 33 (see arrows) flows out into a low-pressure combustion gas passage from a space defined between a side wall of the seal ring 34 provided at the stationary blade 31 and the sealing plate 23 of the moving blade 21 by way of the clearance t formed between the honeycomb seal 38 and the rotor arm portion 25a at the downstream side of the combustion gas flow. As the high pressure leaking air 40 flows along the path mentioned above, resistance to its flow increases. Consequently, a sealing effect takes place between the honeycomb seal 38 and the rotor arm portion 25a which are disposed close to each other, whereby the high temperature combustion gas is prevented from entering the interior of the stationary blade 31. Similarly, the leaking air flows out into a space between the honeycomb seal 37, provided at the stationary blade 31 and disposed at the upstream side of the combustion gas flow, and the rotor arm portion 25b, resulting in increased resistance to the flow of leaking air, whereby sealing is provided for the combustion gas passage.
However, the conventional sealing structure for the gas turbine described above suffers a problem in that since the honeycomb seals 37 and 38 are mounted directly at the end portions of the inner shroud members 32 of the stationary blades 31, nonuniform variation occurs in the clearance t with respect to the circumferential dimension thereof due to deformation of the inner shroud members 32 after operation of the gas turbine, dimensional dispersion of the inner shroud members upon manufacturing or due to other causes. Furthermore, because the rotor arm portions 25a and 25b of the platform 22 which rotate relative to the inner shroud members 32 are each of an annular shape and follow a circular path upon rotation, the clearances t formed between the honeycomb seals 38 and 37 mounted on the inner shroud members 32 and the rotor arm portions 25a and 25b of the platform 22 can not be controlled at all, thus giving rise to a problem.
The situation mentioned above will be explained with reference to the drawings. FIG. 7 is a sectional view taken along the line E--E in FIG. 6. Referring to the figure, a plurality of inner shroud members 32 of the stationary blades 31 are mounted independent of one another in an annular array at an appropriate distance along a circumference, and are spaced from the circular rotor arm portion 25a by a predetermined distance. Moreover, the honeycomb seal 38 is mounted on the inner shroud member 32, and the space between the honeycomb seal 38 and the rotor arm portion 25a represents the clearance t. The state of the inner shroud members 32 immediately after the manufacturing thereof is indicated by solid lines. After operation of the gas turbine, the inner shroud members 32 and the stationary blades 31 undergo deformation due to rotation of the rotor arm portion 25a, as indicated by the broken lines. This deformation causes the honeycomb seal 38 to deviate from its desired position, which in turn brings about variation in the clearance between the honeycomb seal 38 and the rotor arm portion 25a. Accordingly, control of the clearance between the honeycomb seals 38 mounted on the inner shroud members 32 and the rotor arm portion 25a of the platform 22 is made impossible.